Conventionally, as a surface protection film and an interlayer insulating film of a semiconductor device, a polyimide resin which has improved heat resistance, electric properties, mechanical properties or the like in combination has been used. However, as a semiconductor device has become highly integrated and has become larger in size, there has been a demand for a thinner and smaller package for a sealed resin. Under such circumstances, a method for surface mounting such as LOC (lead-on-chip) and reflow soldering has been adapted, and the demand for a polyimide resin which is improved in mechanical properties, heat resistance or the like has become greater than ever.
A photosensitive polyimide obtained by imparting photosensitive properties with a polyimide resin itself has been used. This photosensitive polyimide has advantages that pattern formation steps can be simplified and the time required for complex production can be shortened. A heat-resistant photoresist using a conventional polyimide or its precursor and the application thereof are well known. Regarding a negative-type photoresist, a polyimide obtained by introducing a methacryloyl group into a polyimide precursor through an ester bond or an ionic bond (see JP-B-3712164, JP-A-2006-173655, JP-A-2008-1876 and JP-A-2008-1877, for example), a soluble polyimide having a photopolymerizable olefin (see JP-A-H10-36506, JP-A-2000-159887, JP-A-2000-290372, JP-A-2006-328407, JP-B-3860359 and JP-A-2006-328407, for example) and a self-sensitized polyimide having a benzophenone skeleton and an alkyl group at an ortho group of an aromatic ring to which a nitrogen atom is bonded (see JP-A-2008-251121 and JP-A-2008-310946, for example), or the like are known.
In recent years, use of such photosensitive polyimide in a circuit formation substrate on a suspension in which a magnetic head of a hard disc drive, such as those mentioned below, is mounted has attracted attention.
As for the magnetic head, in respect of an increased memory capacity, an increased speed or the like of a hard disc drive, a so-called MR-thin film composited head in which a magnetic resistive type MR (Magnetic Resistive) device and a thin film is integrated has attracted attention instead of a conventional MIG (metal-in-gap) or magnetic inductive thin film.
In contrast to a conventional head in which reading and writing of a magnetic signal is conducted simultaneously in a single head, in a MR head, writing and reading are conducted separately in a single head. As a result, the number of terminals has been doubled (if need arises, a ground terminal is added), and hence, a wire for connecting a head and a disk main body is required to be thinner.
However, a wire tends to be corroded as it is rendered thinner. In addition, troubles such as difficulty in interface with impedance and difficulty in mounting of a head tend to occur. In order to solve such new problems, a method in which a circuit is directly formed on a suspension in which a head is mounted has been proposed (see JP-A-S48-16620).